Technical Field
The present disclosure relates to a temperature sensing system for a switching device and more particularly, to a temperature sensing system capable of effectively solving a signal processing problem for transmission isolation between an IGBT module which is a substantially high-voltage side and a controller which is a low-voltage side while increasing accuracy of temperature sensing by utilizing diode type IGBT temperature sensing using a diode mounted in an IGBT as a switching device.
Background Art
Generally, environmentally friendly vehicles, such as an electric vehicle, a hybrid electric vehicle, and a fuel cell vehicle, are equipped with a motor system which includes a driving motor for driving a vehicle and an inverter for converting a direct current (DC) voltage from a substantially high voltage power supply into an alternating current (AC) voltage to drive a motor. In this configuration, the driving motor is driven by a 3-phase current which is transferred from the inverter through a power cable and the inverter is configured to switch the switching device with a pulse width modulation (PWM) signal of the controller to convert the DC voltage from the substantially high voltage power supply into the AC voltage.
The switching device used as a power module in the typical inverter includes an insulated gate bipolar transistor (hereinafter, referred to as “IGBT”) which may be configured to perform a high-speed switching operation even when using substantial power. In environmentally friendly vehicles, the above-mentioned inverter as well as a power conversion apparatus such as a direct current to direct current (DC-DC) converter, which has been used in various circuits within a vehicle, makes uses IGBT as the power switching device. Meanwhile, since a capacity of current which is transferred or cut off during the switching operation is substantial, the IGBT module may be damaged due to overtemperature or overcurrent experienced during operation.
Therefore, a temperature sensor configured to measure temperature and which may prevent the IGBT module from being damaged due to conditions such as overtemperature, overcurrent, and the like may be disposed within the IGBT module and in particular, may be disposed on direct bonded copper (DBC) of the IGBT module. For a typical temperature sensor, such as a negative temperature coefficient (NTC) thermistor in which an electric resistance is continuously changed based on a temperature, has been used. The NTC thermistor may be configured to perform temperature sensing using a resistance value which is changed based on temperature. For example, a temperature may be predicted by a voltage difference value measured between the NTC thermistor which is the temperature sensor and another resistor.
However, when using an NTC thermistor, as illustrated in FIG. 1, the temperature of the IGBT module may be sensed and graphed as a non-linear curve, and therefore resolution at a substantially high-temperature, where accuracy may be required is reduced. As a result, accurate sensing of a temperature may be difficult. The NTC thermistor does not directly sense the temperature of the IGBT device but instead, uses an indirect sensing method in when the NTC thermistor is mounted on the DBC, and as a result, accurate measurement of temperature may be difficult. The temperature of the DBC, on which the temperature sensor may be disposed, is approximately the same as that of a cooler (a type of heat sink having a cooling water circulation path provided therein) contacting a bottom surface of the DBC, and as a result, a junction temperature of a semiconductor chip (which generates heat and therefore an electrical signal exchange operation within the IGBT module may not be accurately measured. In other words, for the temperature sensor to measure the junction temperature of the semiconductor chip which generates heat, there is a need to monitor the temperature of cooling water within the cooler contacting the DBC, which may lead to inaccurate junction temperature measurement of the semiconductor chip.
To protect the junction temperature of the semiconductor chip, calculation of the junction temperature is desirable. However, a calculation error may be substantial while estimating the junction temperature using a thermal model and the configuration of such a model has proven to be difficult. When the junction temperature of the semiconductor chip is calculated, the calculated junction temperature may fit a prediction of the junction temperature by a thermal model and the heat value estimation during normally driving the inverter. However, in a hill hold mode, used to prevent a vehicle from going backwards down an uphill road by adjusting a torque of the driving motor by the inverter, estimation of the junction temperature of the semiconductor chip may be difficult and errors occurring at each sample frequency when the variable switching of the inverter are substantial, such that an overtemperature protection operation for the IGBT module including the semiconductor chip may not be accurately performed. The temperature estimation substituted into the logic for protecting the overtemperature and the overcurrent during the failure of the current sensor may be inaccurate and thus the overtemperature protection may not be properly performed. Accordingly, the IGBT module may be damaged while driving the environmentally-friendly vehicle, causing unsafe driving of the vehicle.
A method for embedding a temperature sensor in a semiconductor chip rather than a method for disposing a temperature sensor on a DBC substrate has been developed. In other words, the temperature of the module may be directly sensed and the semiconductor junction temperature may be more precisely measured by mounting a diode, (which may solve non-linear characteristics of the NTC thermistor), in the IGBT semiconductor device. However, accurate temperature sensing may be performed by the diode mounted therein, but there remains a need to electrically isolate the IGBT (which is the substantially high-voltage side) from the control element (which is the low-voltage side), recognizing the temperature using the sensing signal for t safety, thereby improving transmission isolation in aspects of signal processing.
The above information disclosed in this background section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.